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How do you tell the difference between a 350 and a 454?

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  • How do you tell the difference between a 350 and a 454?

    Story: Step-Dad is looking to replace carbs due to one is Edelbrock (non-marine) and one is Rochester Quadrajet Ser# 17059293 (for a 350).

    He is not sure whether the engines are 454 or 350.

    HE says the serial numbers are 28526 and 27699 (which doesn't look right from the numbers i see on sterndrive.info.

    So, where would the serial numbers be so i can look up the block, or.. how can you visibly tell the difference between a 454 and a 350?

    Boat: 1979 Uniflight 36ft Sport Sedan.
    Ben Meyer
    1988 Sea Ray Seville 200

  • #2
    Re: How do you tell the difference between a 350 and a 454?

    Small block and big blocks where Chevy is concerned are so named because of the physical sizes are so different. The Chevy small blocks generally ran from the early 265 cid all the way up to the 400 cid engine. The big blocks ran from a 396 version all the way up to the 454. Now a 396 may displace less than a 400 but put them side by side and you will NOT mistake one for the other. The 396 is a larger engine with respect to external dimensions. Size of the valve covers between the two, the 396 is much larger.
    Spark, Air and Fuel... all you need.... well, and beer!

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    • #3
      Re: How do you tell the difference between a 350 and a 454?

      BBC has flatter, wider looking valve covers.

      Look at the side of the engine, and the exhaust to spark plug orientation.

      SBC: exhaust/sparkplug/sparkplug/exhaust/exhaust/sparkplug/sparkplug/exhaust
      BBC: exhaust/spark/exhaust/spark/exhaust/spark/exhaust/spark
      2005 Rinker Captiva 232
      Merc MAG 350 MPI
      Bravo III Drive 26P Merc SS Prop
      2016 Venture VATB-5225 Aluminum Trailer

      2005 GMC Yukon Denali Tow Vehicle
      2010 Chevy Camaro RS/SS Daily Driver

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      • #4
        Re: How do you tell the difference between a 350 and a 454?

        ^This. The easiest way is by looking at the exhaust manifolds for the exhuast port pattern. If the exhaust ports are evenly spaced it's a BBC, if they middle two ports are closer together than the outer two ports, it's an SBC.
        1976 Mark Twain 200VBR w/Mercruiser 233 (Ford 351w) "Heart & Soul"

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        • #5
          Re: How do you tell the difference between a 350 and a 454?

          And the carbs will not care which you have.

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          • #6
            Re: How do you tell the difference between a 350 and a 454?

            Originally posted by Fishermark View Post
            And the carbs will not care which you have.
            not sure what you mean here..

            however, the manuel says the engine is a ch350rh, 350HP year 1979, and it says 454cid, so i tend to think for sure they are 454s....
            Ben Meyer
            1988 Sea Ray Seville 200

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            • #7
              Re: How do you tell the difference between a 350 and a 454?

              I mean the carb will fit either engine.

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              • #8
                Re: How do you tell the difference between a 350 and a 454?

                however, the manuel says the engine is a ch350rh, 350HP year 1979, and it says 454cid, so i tend to think for sure they are 454s....
                Ayuh,... Then you'll need a pair of Edlebrock 750s....

                The SBC's usually prefer the 600 copies...

                The Edlebrock performer series is a Carbon Copy of the Merc/ Weber carbs still in production...
                But a 'ell of alot Cheaper, 'n easier to get tuning parts for...
                The Edlebrock kits work Perfectly in my Merc/ Webers...

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                • #9
                  Sign up today
                  Re: How do you tell the difference between a 350 and a 454?

                  Post a picture of your engines. Many here can tell the difference with just a quick glance.
                  If they are Mercruiser, and I would guess they are MIE (inboards) and not IO's, there should be a metal tag just above and slightly aft of the starter.
                  Don S.


                  Please, no PM's (Private Messages) regarding boat/engine problems.
                  That is what the forums are for.
                  Only forum/moderator issues will be answered in PM's.

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